Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $242.87   10.437%   $268.2183   $268.22   $268.20   $268.20  
  Purchase #2 $41.93   12.574%   $47.2023   $47.20   $47.20   $47.20  
  Purchase #3 $147.83   13.503%   $167.7915   $167.79   $167.80   $167.80  
  Purchase #4 $87.57   10.550%   $96.8086   $96.81   $96.80   $96.80  
  Purchase #5 $242.64   6.668%   $258.8192   $258.82   $258.80   $258.80  
  Purchase #6 $48.48   9.681%   $53.1733   $53.17   $53.15   $53.20  
  Purchase #7 $56.74   13.714%   $64.5213   $64.52   $64.50   $64.50  
  7 purchase totals = $868.06       $956.5345   $956.53   $956.45   $956.50